Cell cycle checkpoint status in human malignant mesothelioma cell lines: response to gamma radiation

Knowledge of the function of the cell cycle checkpoints in tumour cells may be important to develop treatment strategies for human cancers. The protein p53 is an important factor that regulates cell cycle progression and apoptosis in response to drugs. In human malignant mesothelioma, p53 is generally not mutated, but may be inactivated by SV40 early region T antigen (SV40 Tag). However, the function of p53 has not been investigated in mesothelioma cells. Here, we investigated the function of the cell cycle checkpoints in six human mesothelioma cell lines (HMCLs) by studying the cell distribution in the different phases of the cell cycle by flow cytometry, and expression of cell cycle proteins, p53, p21WAF1/CIP1 and p27KIP1. In addition, we studied p53 gene mutations and expression of SV40 Tag. After exposure to γ-radiation, HMCLs were arrested either in one or both phases of the cell cycle, demonstrating a heterogeneity in cell cycle control. G1 arrest was p21WAF1/CIP1- and p53-dependent. Lack of arrest in G1 was not related to p53 mutation or binding to SV40 Tag, except in one HMCL presenting a missense mutation at codon 248. These results may help us to understand mesothelioma and develop new treatments

In vitro response of rat pleural mesothelial cells to talc samples in genotoxicity assays (sister chromatid exchanges and DNA repair)

International audienceThe genotoxicity of three samples of talc has been determined using in vitro cell systems previously developed for testing asbestos fibres. The talc samples used consisted of particles of respirable size in order to test the effect of particles likely to be deposited in the lung. Genotoxicity was tested in cultures of rat pleural mesothelial cells (RPMC) using genotoxicity assays for unscheduled DNA synthesis (UDS) and sister chromatid exchanges (SCEs). The effects were compared with those obtained with negative controls (attapulgite and anatase) and positive controls (chrysotile and crocidolite asbestos). In contrast to asbestos, none of the talc samples, nor the negative controls, induced enhancement of UDS or SCEs in treated cultures in comparison with the untreated cultures

: Anoikis resistance of mesothelioma cells

International audiencePleural fluid accumulation is a frequent clinical observation in diffuse malignant pleural mesothelioma (MPM). The cytological analysis of pleural fluid often reveals the presence of free spheroid aggregates of malignant cells, giving rise to the question of the ability of non-adherent tumor cells to resist the loss of anchorage-induced apoptosis (termed as anoikis), and to develop new tumor foci in the pleural cavity. Here, we show that MPM cells cultured under non-adherent conditions form well-organized aggregates composed of viable cells, which progressively enter in G(0). Although the PI3K/Akt, ERK and SAPK/JNK signaling pathways are activated in adherent MPM cells, loss of anchorage results in the inactivation of these pathways. By comparison, we show that the non-tumoral mesothelial cells MeT-5A enter anoikis in an SAPK/JNK-, Bim- and caspase-9-dependent pathway. The survival of MPM cells can be reversed by activating SAPK/JNK with anisomycin, according to a Bim-dependent mitochondrial pathway. Finally, our findings show that impairment of cell aggregation activates SAPK/JNK and Bim and induces anoikis. Our results underline the importance of intercellular contacts in the anoikis resistance of MPM cells